Coating composition containing a fatty acid ester as a gel stabilizing agent



Patented Apr. 12, 1949 COATING COMPOSITION CONTAINING A FATTY ACID ESTERAS A GEL STABILIZ- ING AGENT Emile E. Habib, Belmont, and David G.Greenlie, Wayland, Mass., assignors to Dewey and Almy Chemical Company,North Cambridge, Mass., a corporation of Massachusetts No Drawing.Application May 20, 1947, Serial No. 749,340. In Canada May 11, 1944 1Claims. (01. zen-23.5)

1 This invention relates to coating compositions particularly tocompositions of wax and other materials designed .to be spread oncardboard, paper or fabrics to make the material moisture andvaper-proof.

Parafiin wax has commonly been used for this purpose but parafiin waxdoes not make a completely moistureproof coating because Water vapor maypass through the coating along the paraiiln crystal boundaries. Toprevent moisture from penetrating, a carton water-proofing materialwhich impregnates cardboard is not as satis factory as one which forms acontinuous film on the surface of the carton provided the surface filmis flexible. The reason is that when all of the free space in thecardboard is occupied by wax and the carton is then dented or bent, thecrystal structure snaps at the. point of greatest strain. Although allof the fibres may not be ruptured across the break, passageways areopened which permit moisture toenter. A film, on the other hand, maydistort without; rupture. The canton does not split or tear as easilybecause the fibres are free to move in the free space between the fibresand are not immediately sheared by an impact as happens when fibres arerigidly held in a matrix of impregnating material.

A composition which coats rather than impregnates the board also hasadvantages because of its economy. Less material is required to coat theboard than to impregnate the whole mass. Paramn, however, impregnatespaperboard and consequently certain compositions have appeared in anattempt to modify paraflin so that it will form surface films on theboard yet not impregnate it to any substantial degree. Among the moresatisfactory compositions for this purpose are mixtures of paraflin orpetroleum waxes and an especially depolymerized rubber. Seemingly thiscombination works because the rubber has gone into a solvated state inthe wax and exists in the mixture as a solvated colloidal gel. The gelstructure traps and holds the wax on the surface where it solidifiesinto a continuous film. This coating makes a package which isspectacularly vaporproof, does not block, and is sufficient- -lyflexible to withstand rough handling at'room temperatures but the gelwhen subjected to long continued heating as is necessary when dipping orcoating cartons is in progress, is unstable.

The objects of this invention are to produce coating compositions whichare moisture and vaporproof, which coat rather than impregnate fibroussurfaces, which have high stability in the dipping kettles, which willnot sediment, which at the present time require no critical materials intheir manufacture and which provide a range of coating compositions fromcompositions which will neither check nor chip off the board at 20 F. tohard non-blocking coatings at +l F. Formulas compounded according to thepresent invention successfully meet these requirements.

Surprisingly, when numerous resins were added. to the paraflin in orderto increase its viscosity and prevent penetration into the paperboardthe rise in viscosity did not inhibit penetration of the compound intothe board. In many cases the absorption is even greater when resin isadded to the parafiin than when no resin is present. This ischaracteristic of a wide variety of resins including the coumarone-inden.type, rosin, and Vinsol resin, the latter being a gasolineinsolubleresin derived from the dark colored residue concurrentlyremoved with F. F. wood rosin after extraction of pine chips with a coaltar hydrocarbon such, for instance, as benzene, toluene, xylene (seePatents Nos. 2,287,351 and 2,287,352). It contrasts markedly with theperformance of depolymerized rubber. Consequently it was believed thatto prevent the penetration of the parafiin into the paperboard amaterial other than rubber should be one which sium, aluminum stearateWas found to be the most satisfactory for increasing the viscosity ofthe material when only a small amount was used. For example, a gelcomposed of 5% aluminum stearate in paraflin penetrates newsprintscarcely at all. However, if this mixture is maintained at 200 F. forforty-eight hours, the original viscosity drops progressively until itis only slightly greater than that of the paraffin. The gel alsogradually disappears and the aluminum stea-rate separates as a flakysediment. After such ageing, this compound penetrates the board asreadily as does uncompounded paraffin wax.

We have discovered that the separation of water insoluble metallicsoaps, particularly alumi num stearate, from the compound may beprevented and that a substantially stable viscosity may be given. to thecompound by adding to the composition fatty-acid esters of monoanddianhydro-hexahydric alcohols in which the fatty acid contains from 12to 18 carbon atoms. Tests made using all esters which are commerciallyavailable at present show that the stabilization imparted to the waxstearate com-position is a general. property of fatty-acid esters ofmonoand di-anhydro-hexahydric alcohols.

We prefer, because of present availability, to use mannide dioleate orits stereoisomer sorbide dioleate, but the following range of materialshave already given operative results: mannitan mono-oleate, sorbitanmono-oleate, sorbitan dioleate, sorbitan trioleate, sorbitantetraoleate, sorbitan monostearate, sorbitan distearate, sorbitantetrastearate, mannide dioleate, mannide monolaurate, mannidedipalmitate, mannide monostearate, sorbide dioleate and sorbitanmonolaurate and mixtures of the foregoing.

When these materials are added to the metallic soap-wax composition,excellent stability is achieved. In the first four hours after theaddition the viscosity drops slightly. Thereafter the compound may besubjected to holding temperatures of 200 F. in the dip tanks with noprecipitation of the gel. For most uses the parailln-stearate compoundwill be found too brittle, but it may be plasticized by the addition ofan organic plasticizer. This may be a compatible resin, among others,those listed above, or an appropriate proportion of mlcrocrystallinewax-or both. Because of its availability and constant performance, weprefer polymerized B-pinene.

The term petroleum wax is; intended to cover the group of wax-likepetroleum hydrocarbons including the crystalline paraflin waxes and theso-called amorphous or microcrystalline petroleum waxes which frequentlyare produced by further refining of petrolatum.

The stability which is given to the gel of a metallic soap in petroleumwax by the higher fatty-acid esters described above is imparted to thewhole range of such waxes. Our invention contemplates that the wax mayeither be parafiin or microcrystalline (amorphous) waxes or mixtures ofthe two in any proportions which are necessary to give whatever heat orcold resistance may be demanded. The following examples show how thecoatings may be adapted to various temperature conditions by a properselection of the melting point of the waxes and the mutual proportionswhich are employed. Our preferred examples are given as follows:

Example 1 Example 2 A composition which will not block at +130 F. butresists +20 F. is made by substituting 146 F. M. P. paraiiln for the 135F. M. P. Paraflln of Ex. 1.

' Example 3 A compound which will neither check nor chip of! the boardat -20 F. but will block at about 110 F. is made by following the sameprocedure as in Example 1 save for (e) where paraffin wax (M. P. 135 F.)593 parts, microcrystalline petroleum wax (M. P. 152 F.) 400 parts, areused.

Example 4 A compound which remains flexible at 20 F. but blocks at 70 F.is made as follows:

Example 5 The stabilizing properties of a series of anhydrohexahydricalcohol fatty acid esters were tested as follows: 100 parts by weight ofparamn wax (M. P. 135 F.) were heated to 170-180 F., and 3.3 partsaluminum stearate stirred into the wax until dissolved. The stabilizingagent was then added and the mixture heated with stirring to 240 F. Theviscosity of the mixture was read 1 while hot, again after cooling andremelting, and

115 F.) are pulverized and added with stirring to (c).

813 parts of paraflin (M. P. 135 F.) 200 parts of amorphous' petroleumwax M. P. 158-60 are melted together at 210 F. The product of step (d)is then added to this mixture and stirring is continued until thetemperature drops to 175-1'70 F. The mass is then run out into shippingcontainers.

This compound will neither check'nor chip ofi paperboard at +5 F. Itwill not block at F. It solidifies at -134" F. Its viscosity (cupmethod) at F. is 13-15 seconds.

at successive intervals after storage at elevated temperature. In thestorage-stability results, excellent denotes a composition which main.-tained its viscosity throughout the conditions of the test with onlyslight variations; while good refers to a composition whose originalviscosity was lowered, but whose final viscosity was substantiallyhigher than that of unstabilized compounds. In no case did the aluminumstearate settle out of the mixture.

- Parts by Stability on Stabmzer Weight Storage Mannitan mono-oleate l.54 excellent. Sorbitan mono-oleate. l. 54 Do. Sorbitan dioleate. 2. 66Do. Sorbitan trioleate 3.89 Do. Sorbitan tetraoleate- 5. 30 good.Sorbitan monostearate l. 54 excellent Sorbitan dlstearate. 2. 66 Do.Sorbitan tetrastearate. 5. 30 Do. Mannide dioleate 2.93 good. Mannidemonolaurate 1. 32 Do. Mannide dipalmitate 2. 69 Do. Mannidemonostearate. l. 67 Do. Sorbide dioleate- 2. 93 excellent. Sorbitanmonolaurate 1. 24 Do.

Microscopic studies on the crystal structure of the coating show thatthe size of the crystals is greatly reduced when our invention ispracticed. Progressive crystal growth is inhibited, probably because ofthe presence on the crystal surfaces of a material which is not solublein the wax. The coatings made from these materials when spread oncardboard, paper, or fabrics are dense and highly vapor and gas proof.

This application is a continuation-in-part of our co-pending applicationSerial No. 486,584,

filed May 11, 1943, now abandoned.

taing from 12 to 18 carbon atoms, said composiy tion being in the formof a gel.

2. A coating composition comprising a petroleum wax, a water-insolublemetal soap, a gelstabilizing agent selected from the class consisting offatty acid esters of monoand di-anhydrohexahydric alcohols, the fattyacid containing from 12 to 18 carbon atoms, and a compatible organicplasticizer, said composition being in the form of a gel.

3. A coating composition comprising a mixture of a paraffin wax, amicrocrystalline wax, a waterinsoluble metal soap, sorbide dioleate, anda compatible organic plasticizer, said composition being in the form ofa gel.

4. A coating composition comprising a petroleum wax, aluminum stearate,sorbide dioleate, and polymerized B-pinene, said composition being inthe form of a. gel.

5. A coating composition comprising a petroleum wax, a water-insolublemetal soap, and an oleic acid ester of an anhydro-hexahydric alcohol,said composition being in the form of a gel.

6. A coating composition comprising a petroleum wax, a water-insolublemetal soap, and a stearic acid ester of an anhydro-hexahydric alcohol,said composition being in the form of a gel.

7. A coating composition comprising a petroleum wax, a. water-insolublemetal soap, and a lauric acid ester of an anhydro-hexahydric alcohol,said composition being in the form of a gel.

EMILE E. HABIB. DAVID GREENLIE.

REFERENCES crrEn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,334,709 Katzman et al Nov. 23,1943 2,348,689 Abrams et a1 May 9, 1944

